This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A334890 #11 Jul 16 2025 07:10:32
%S A334890 1,-1,-1,-2,-1,-4,-1,-2,-3,-6,-1,-1,-1,-8,-7,0,-1,-4,-1,-3,-9,-12,-1,
%T A334890 14,-5,-14,-6,-5,-1,-2,-1,4,-13,-18,-11,28,-1,-20,-15,18,-1,-6,-1,-9,
%U A334890 -10,-24,-1,36,-7,-18,-19,-11,-1,12,-15,22,-21,-30,-1,85,-1,-32,-14,8,-17
%N A334890 a(1) = 1; a(n) = -Sum_{d|n, d > 1} (sigma(d) - d) * a(n/d).
%H A334890 Vaclav Kotesovec, <a href="/A334890/b334890.txt">Table of n, a(n) for n = 1..10000</a>
%F A334890 G.f. A(x) satisfies: A(x) = x - Sum_{k>=2} A001065(k) * A(x^k).
%F A334890 Dirichlet g.f.: 1 / (1 + zeta(s-1) * (zeta(s) - 1)).
%t A334890 a[n_] := If[n == 1, n, -Sum[If[d > 1, (DivisorSigma[1, d] - d) a[n/d], 0], {d, Divisors[n]}]]; Table[a[n], {n, 65}]
%o A334890 (PARI) lista(nn) = {my(va=vector(nn)); va[1] = 1; for (n=2, nn, va[n] = -sumdiv(n, d, if (d>1, (sigma(d) - d) * va[n/d]));); va;} \\ _Michel Marcus_, May 15 2020
%Y A334890 Cf. A000203, A001065, A046692, A305807.
%K A334890 sign
%O A334890 1,4
%A A334890 _Ilya Gutkovskiy_, May 14 2020